A facile and economic route assisted by trace tannic acid to construct a high-performance thin film composite NF membrane for desalination

Abstract

Tailoring the structure and properties of the polyamide (PA) layer in a straightforward way is considered promising for fabricating advanced thin film composite (TFC) nanofiltration (NF) membranes. Herein, green and cost-effective tannic acid (TA) was used as an effective additive in the aqueous phase to construct TFC NF membranes via interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). It was found that the introduction of a small quantity of TA could alter the IP process by attracting more PIP monomers, locally enriching them on the substrate and hindering their diffusion toward the water/organic interface via protonation reaction and hydrogen bonding, resulting in a rough and dense PA structure. Besides, characterizations confirmed that the proper incorporation of TA improved the membrane cross-linking degree, surface hydrophilicity and electronegativity. Consequently, the optimal TFC membrane, obtained at a low TA concentration of 0.004 w/v%, exhibited superior separation performance with permeate fluxes of 67.1 LMH and 55.7 LMH and rejections of 97.0% and 94.4% for Na₂SO₄ and MgSO₄ solutions, respectively. Notably, the optimized TFC membrane outperformed its control counterparts, indicating the efficiency of TA incorporation in constructing a high-performance TFC NF membrane. This work provides a straightforward and economic route to fabricate competitive dense NF membranes for water purification.